The invention relates, in general, to a pallet container and more particularly to a pallet container of a type having a thin-walled rigid inner receptacle, preferably made from thermoplastic material for the storage and transport of liquid or free-flowing goods, wherein the plastic container is closely surrounded by an outer cage jacket as a supporting casing for the plastic container and a bottom pallet on which the thermoplastic receptacle is supported and which is firmly secured to the supporting casing.
Pallet containers of the type having a support jacket such as for example a wire cage jacket type or a cage jacket with horizontal and vertical bars are generally known in the prior art; e.g. from U.S. Pat. No. 4,676,373 (Schn./W).
The cage jackets in the pallet containers of the prior art are secured to the bottom pallet, which may be configured as a flat pallet from plastic or wood, or as a steel bar frame and is usually realized by fastening means such as for example, screws, brackets, clamps, clasps or claws that engage the lower horizontally surrounding cage bars. These fasteners are usually nailed, riveted, pinned screwed or welded to the upper plate or the upper outer edge of the pallet. In case where the pallet container has a support jacket of the bar cage jacket type, the cage bars can be configured as open or closed profiles having round cross section or rectangular cross section.
For industrial use, the pallet containers have to pass an official approval inspection and meet certain quality criteria. For example, the filled pallet containers have to undergo interior pressure tests and drop tests from specific heights, which are also conducted at extremely low temperatures (xe2x88x9220xc2x0 C.). The worst case drop is a diagonal drop onto the lower pallet end side, which carries the bottom outlet valve of the inner plastic receptacle.
As has been shown in such drop tests, the inner plastic receptacle tends to shift relative to the bottom pallet during ground impact. Through the kinetic impact energy, especially at the impact end wall, the bars become severely deformed and in neighboring lateral peripheral regions are partly torn from the bottom pallet. The securement of the lower rim of the cage jacket to the bottom pallet thus is a crucial problem area. Since the attachment of the cage jacket is provided only at a few areas, the cage jacket, especially when a bar cage is involved, is deformed very unevenly and warps, whereby the thin-walled plastic receptacle can be damaged by torn off cage parts.
Pallet containers or combination-IBCs (IBC=Intermediate Bulk Container) of the type involved here are used for transporting liquids. Preferably, they usually have a filling volume of 1000 liters and consist of a pallet, a cage jacket, which is attached to the bottom pallet, and an inner receptacle made from PE-HD, which is firmly surrounded by the cage jacket, and which has an upper fill opening and a lower outlet fitting.
Upon diagonal drop testing at the lower critical pallet end face (the area where the outlet fitting of the inner container is disposed), the inner container with the liquid content has the tendency of lateral slipping and shifting in the direction of the forward or lower cage wall. The surge forces of the content and the thrust force of the inner container must be absorbed primarily by the forward cage wall. As a result of the ground impact of a filled pallet container during the diagonal drop test quite significant elastic and plastic, i.e. permanent, deformations are incurred; which lead to catastrophic deformations and damage to the inner container, when the cage jacket and pallet have insufficient strength. The area around the outlet fitting is hereby predominantly at risk.
The test conditions during drop testing include that the inner container must be absolutely tight, without leakage of any content from the outlet fitting or from the overstressed stretching areas of the inner plastic container, and that the pallet container is still maneuverable, i.e. that it can be picked up by a fork lift and be able to be transported. These are essential preconditions for the pallet container to receive official approval for use with hazardous liquid contents.
According to one aspect of the present invention, an improved pallet container is provided which is designed to obviate the afore-stated shortcomings and drawbacks and which is configured with improved drop impact stability and increased strength against mechanical stress, in particular high drop strength, and which achieves with simple constructive means a decrease of transverse forces on the wall of the cage-like bar frame during diagonal drop.
Another aspect of the present invention is to provide a pallet container suitable for transporting dangerous liquids up to the highest standard of quality to thereby enable issuance of a respective official permit for the pallet container for application or use with liquids in the upper hazard class.
These aspects, and others which will become apparent hereinafter, are attained in accordance with the present invention wherein a pallet container comprises a bottom pallet; a thin-walled rigid inner receptacle for storage and transport of liquid or free-flowing contents; and a cage-like bar frame closely surrounding the receptacle and securely connected with the bottom pallet, wherein the surface area of the bottom pallet which is bounded by the support area of the inner plastic container, or optionally an intermediate plate disposed between the surface area of the bottom pallet and the outer surface of the inner container bottom, is provided with means for increasing slip resistance relative to the horizontal plane, between a downwardly pointing outer surface of the inner container bottom and an upwardly pointing surface of the bottom pallet.
The pallet container according to the invention is based on the recognition that the comparably smooth bottom of the inner plastic container does not have a substantial slip resistance upon the comparably smooth surface of the bottom pallet or an intermediate plate disposed, optionally in-between e.g. as dampening element or as support plate of sheet metal or plastic, e.g. foamed polystyrene on a metal frame pallet, when the pallet container is positioned at an inclination and in particular during a diagonal drop, so that the filled inner container is able to slide to the side without appreciable friction resistance. By providing the afore-described surfaces with slip-resistant or slip-reducing means it has been found that at a diagonal ground impact, the kinetic energy within the dropping filled inner plastic container is consumed at least in part by the friction increasing means and the entire impact energy does not have to be absorbed by the lower cage basket wall.
As a consequence, the inner container is substantially prevented from shifting relative to the pallet during the drop test, and stress relief of the forward and lower support frame is realized. As a result, less deformation occurs with the cage frame of a pallet container configured in accordance with the invention which makes the pallet container suitable for application with hazardous liquid and flowable contents up to class 6, the highest approval quality.
According to one embodiment of the invention, the bottom wall of the inner plastic container is provided with projections which project outwards i.e. downwards, and respective dimples, which are formed in the surface of the intermediate plate or/and in the surface of the bottom pallet and point inwards i.e. downwards, for interlocking engagement in positive manner.
The pallet container known from the afore-mentioned U.S. Pat. No. 4,676,373 discloses a collecting trough which is inset in mid-section of the bottom wall of the inner container between two pallet boards of a wood pallet and extending to the outlet valve, however, this inset collecting trough is not bounded within the support surface inner container/bottom pallet but rather extends to the forward edge of the bottom pallet. Since it does not extend across, the collecting trough does not provide protection for the outlet valve as the inner container can slip unimpeded in the direction of the forward pallet edge. An effective positive connection within the meaning of the present invention, i.e. transverse to the direction of the forward pallet edge for protection of the outlet valve, is neither provided nor suggested.
According to another preferred embodiment of the invention, dimples, which point inwards i.e. upwards are provided within the bottom wall of the inner plastic container, and projections, which are formed in the surface of the intermediate plate or/and in the surface of the bottom pallet and point outwards i.e. upwards, for interlocking engagement in positive manner to thereby establish a form-fitting connection. In order to provide a sufficient effect as xe2x80x9cslip brakexe2x80x9d, the interlocking form-fitting elements (anti slip elements) should have an engagement height of about 5 mm to 50 mm, preferably about 20 mm.
The form-fitting elements can hereby advantageously be slanted to the side to permit a slide-off of the inner container in extreme load situations and to thereby preclude a tearing of the plastic bottom wall. The slant of the form-fitting elements should have an angle between about 45xc2x0 and 85xc2x0, preferably about 80xc2x0.
According to a further embodiment of the invention, the form-fitting elements have an outwardly limited flat extension within the support surface of the inner plastic container upon the bottom pallet and are configured, e.g. as circular, triangular or polygonal form-fitting element. According to another variation, the form-fitting elements may have a linear extension and configured, e.g., as circular, triangular, polygonal or cross-shaped form-fitting element, which is open at least to one side to enable also an emptying of residue.
The form-fitting elements include elevations on the pallet surface and respective indentations in the support surface of the inner container bottom, or elevations, i.e. projections, in the support surface of the inner container bottom and respective recesses (=indentations) in the pallet surface. Both variations may be realized side-by-side at the same time.
The inventive form-fitting elements, arranged within the support surface and outwardly limited, effectively inhibit or reduce a slip-off of the inner container in all possible directions.
A form-fitting element may be made, e.g., of a flat metal plate, plastic plate or wooden plate, having a downwardly projecting pin e.g. with having a diameter of about 200 mm, height of about 30 mm, pin diameter of about 25 mm, pin height of about 40 mm. The pallet surface has formed therein, e.g. at four locations corresponding indentations for example bores, for insertion of the pins of the form-fitting elements. The support surface of the bottom of the inner container must then have corresponding dimples or indentations at respective locations. In this simple manner, each existing bottom pallet of wood, plastic or steel, can be retrofitted for such pallet containers, e.g., when reconditioning a used pallet container and then utilizing a new inner container with respective dimples in the bottom.
According to a preferred embodiment, the bottom of the inner container is constructed along the central pinch-off seam with at least one outwardly i.e. downwardly projecting pin projection which engages in a corresponding recess or slit in the top of the bottom pallet or interposed intermediate plate, and is secured, e.g., by means of a pin inserted transversely at the underside of the pallet deck. In this way, the common disadvantage of an upward pulling of the bottom of the inner container, as a result of shrinkage stress in the thicker pinch-off seam, and impediment to a complete emptying of residue from the inner container are further prevented.